Just looking at buying a used Deuter Comfy Kid III backpack frame style carrier and wondering if it's a totally bad idea or not.

Backstory: I had a broken neck and sinal decompression and fusion surgery 6 years ago- fused from c4 thru c6.
My son is 10 months 24 lbs and I have worn him ocassionally last summer in an Ergo, on the front when he was up to 19 lbs with no problems.
I have a job opportunity for the summer working in a vineyard, good opportunity for me and I would be able to take him with me to work. I would work only from 8 am til noon. I am a single parent and finding childcare is not really an option as I would already be paying full price to hold his spot in dc in a different province. I would just be relocating for 6 weeks with him for this job, room and board provided, but it's out in the boonies so do daycares.

The vineyard is all fenced, steep terrain, but I would also have a stroller with me, but prob back in the truck, for him to nap in.

The frame backpack appeals to me because I could also take it off and he could sleep in it like a little chair at the end of the rows if needed (if my back started to kill me). I have not been able to successfully get him into a back carry with the Ergo because it involves twisting my back and I just don't seem to be able to do this. Also, I am freaked out because I will never have a spotter or anyone to help me get him on or off....so the frame pack seems like the best route.

I borrowed a MEC Happy Trails frame back pack from a friend to try and he loves it. i find it okay on my neck and shoulders...it for sure transfers all the weight to my hips....but my hips are crazy sore after just a short jaunt around the block because of pressure points from the frame. I tried adjusting the torso length to make it ride higher on my back, but it doesn't seem to help.

I found the Deuter version 3 on Kijiji for $180 and it has this moveable joint in the hip belt that allows it to move with your hips.
I am wondering if this is why the other pack is causing hip pain....it is a lot cheaper (I could get one for $50) but not sure it would be worth it if I'm in for hip pain. Just not sure about dropping $180 bucks to just use the Deuter for 45 days.

Does anyone know:

1. How to adjust MEC Happy Trails pack at the hips to reduce pressure points? Maybe add some neoprene pads or something....but is that safe to do?

2. How the Deuter is after a 2-3 hour hike? (Seems great at first but I have no opportunity for an extended trial of it.)

3. If there is some other pack that is better that I haven't considered? I don't know much about babywearing, as do it out of necessity only due to neck pain.

4. Is there some way to safely "trick out" an Ergo with a frame from a MEC Happy Trails pack?

I figure my son will probably ride in pack 1 hour, run up and down rows and play at least another hour, maybe sleep in stroller for an hour and ride in pack another hour....so maybe it won't be so bad if not continous???

Thanks in advance. I have very limited experience with babywearing and not interested in a wrap with loose hanging bits of fabric as this is a safety concern for me while working, and would never be able to figure that out anyhow.